1. Field of the Invention
The present invention relates to an optical pickup and an optical information recording and reproducing apparatus, and, for instance, to an optical pickup for recording and reproducing of a multilayer optical disc including a plurality of recording layers and an optical information recording and reproducing apparatus mounted with the optical pickup.
2. Background Art
The optical information recording and reproducing apparatus has functions of recording information, such as music, video and various pieces of data, and reproducing the information onto and from an optical disc.
As to the optical disc, Blu-ray Disc (BD) including a blue semiconductor laser and a high NA objective lens has become commercially viable. In order to further increase capacity, commercialization of a multilayer optical disc, which includes a plurality of information recording layers, is planned.
However, the multilayer optical disc has a problem of interlayer crosstalk, in which reflected by a non-target layer other than a target layer for recording and reproduction leaks into a detector, thereby adversely affecting a servo signal. Hereinafter, a recording layer as a recording/reproducing target is referred to as a target layer, a recording layer other than the target layer is referred to as a non-target layer.
An optical disc apparatus causes an optical detector to receive light reflected from an optical disc, and generates a reproduction RF signal (RFS: radio frequency signal), a focus error signal (FES) and a tracking error signal (TES) from a detection signal according to an amount of received light. Tracking error (TE) detection methods include a differential push-pull (DPP) method and a differential phase detection (DPD) method. Focus error (FE) detection methods include an astigmatism method, a spot size detection (SSD) method and a knife edge method. Here, the SSD method is disclosed in JP 2008-287851A, and the knife edge method is disclosed in JP 2010-61751A (corresponding to US 2010/0061202 A) and JP 2009-170087A.
FIG. 1 shows examples of diffraction gratings and optical detectors of SSD and knife edge methods for detecting FE. FIG. 1 (i) shows a case of the SSD method. FIGS. 1 (ii) and (iii) show cases of the knife edge methods. (a) and (b) of FIGS. 1 (i) to (iii) correspond to a diffraction grating and an FES detector arrangement, respectively. FIGS. 1 (ii) and (iii) are different from each other in regions (shown by bold frames) of reflected light for detecting FE. In FIG. 1 (ii), detection is performed from reflected light in regions other than a central region of the reflected light and other than a push-pull (PP) region (knife edge method A). In FIG. 1 (iii), detection is performed from reflected light in a PP region (knife edge method B). As to a recording disc, in a case where an incident light spot is at a detracking position, balance of the amount of light in a PP region varies. Accordingly, it is required to suppress adverse effects on FE detection owing to detracking. Thus, in the SSD method, a division line of a detector, or the regions divided as strips, is arranged to be a radial direction (Rad. direction) of an optical disc. In the knife edge method, the longitudinal direction of strips of two divided receiving light regions for detecting defocusing of one spot is arranged to be the Rad. direction; the direction in which the divided receiving light regions are arranged is oriented to be a tangential direction (Tan. direction) of the optical disc, which is orthogonal to the longitudinal direction of the strip.
Techniques on measures against interlayer crosstalk, which becomes a problem when recording and reproducing are performed onto and from a multilayer optical disc, are disclosed for instance in JP 2008-287851A, JP 2010-61751A and JP 2009-170087A. Any of these techniques adopts a one beam pickup, employs a diffraction optical element for addressing interlayer crosstalk, and detects +1-order or higher order diffraction light or −1 or lower order diffraction light, thereby separating stray light from signal light.